Sunday, September 30, 2012

Richard Feynman once remarked that experimental particle physics is somewhat akin to smashing watches together, and examining the various gears, cogs and springs which fly out, in order to better understand how such an intricate device is first put together.

Inspired by his academic counterpart, one can only assume that Michael Schumacher has recently developed a deep interest in the transmission internals and rear-wing assembly of a Formula One car, and wishes to better understand how they are put together.

Hurtling down Esplanade Drive at the re-start of last week's Singapore Grand Prix, approaching the ninety-degree right of turn 14, Michael appeared either to mis-judge his braking, or under-anticipate the braking point of those on worn tyres ahead of him. Locking up all four wheels, and slewing marginally sideways, Michael plunged into the rear of Jean-Eric Vergne's Toro Rosso.

On time-scales brief to the human eye, this triggered a complex hierarchy of energy degrading processes over a range of different length-scales. The front-wing of the Mercedes broke off and partially shattered as the nose of the Mercedes was driven into the rear of the Italian car, lifting it into the air. As the Mercedes rode up and over the rear crash structure on the Toro Rosso, the detached front-wing was briefly trapped under the rear of Vergne's car. The front wheels of the Mercedes folded inwards, the rear-wing of the Toro Rosso shattered into a characteristic fragment-size distribution (large numbers of small fragments, small number of large fragments), and a titanium end-plate of the Mercedes front-wing was simultaneously dragged along the road, raising a cascade of sparks, diffraction-spiked in subsequent photos like an astrophysical star cluster. It was a frightening freeze-frame moment of beautiful complexity.

The ultimate cause of the accident, however, may lie with a comment Schumacher made in the October issue of F1 Racing magazine. Here, Michael was quizzed with readers' questions, and at one point was asked if, looking back over his career, he had any regrets. The answer was terse, but revealing:

"Jerez. In 1997."

Now, far from being a confession or admission, this actually constituted an implicit rebuttal. Michael was, in effect, saying that he doesn't regret any of the litany of other transgressions of which he is often accused: the other deliberate accidents; the dragging of wounded cars back onto the track to get races red-flagged; the deliberate blocking of the track in final qualifying, etc etc. None of that is regretted, presumably because Michael was only stripped of points for that one incident in 1997, when, as Nigel Roebuck put it, the FIA came down on him "like a tonne of feathers."

Michael's latest denial was only going to provoke further action from the Karma Police, who've had the former wunderkind in their cross-hairs for some time now. The combination of circumstances on the restart at Singapore was simply their latest move; an elegantly planned and executed slice of 'fate'.

Elsewhere in the same interview, Michael was asked if there was something which irritates him about Formula One today, and his response was somewhat enigmatic: "Black gold." Prompted to elaborate, Michael merely added "Think about it."

Could Michael possibly be expressing concern about the use of petroleum-derived energy sources in Formula One? Surely not; after all, the total greenhouse gas emissions from the sport are an infinitesimal fraction of global emissions, and McLaren Pan-Galactic, for one, announced late last year that they're actually a carbon-neutral organisation.

Perusing the list of other possible referents for 'black gold', one's eye immediately alights upon that notoriously polarizing condiment, marmite. Joining up the dots to understand Michael's source of vexation, it should be remembered that Lewis Hamilton is Formula One's Mr Marmite: loved by some, loathed by others.

And, as we all found out on Friday this week, Michael's marmite discomfort transpired to be fully justified.

Saturday, September 22, 2012

A recent BBC Horizon documentary on the smallest things in the universe, claimed to present experimental proof that the electron has been split.

With the tone of indulgent bemusement that characterises contemporary television accounts of modern physics, the viewer was told that, in principle, it is possible to split the fundamental properties of the electron. These properties, we were told, are (intrinsic) spin, (electric) charge and orbital (angular momentum), and in the experiment in question, "when the x-ray beam strikes, the electron split into new quasi-particles, called spinons, orbitons and holons, which carry the properties of the electron, and can travel off in different directions."

In point of fact, the electron hasn't been split at all. Quasi-particles are collective excitations in the state of condensed matter, typically the atomic lattice of a crystal. Some of these collective states possess properties which formally resemble properties possessed by states of the individual electron. In 1996, holons and spinons were produced for the first time in the collective state of a crystal, and now a new collective state, containing orbitons and spinons, has been created.

Quasi-particles, however, are certainly of very deep interest, not least because they reveal that particle-like entities can be created as nothing more than transient disturbances within a substrate. As philosopher of physics David Wallace points out, quasi-particles "can be created and annihilated; they can be scattered off one another; they can be detected (by, for instance, scattering them off 'real' particles like neutrons); sometimes we can even measure their time of flight...We have no more evidence than this that 'real' particles exist...and yet they consist only of a certain pattern within the constituents of the solid-state system in question," (p51, The Emergent Multiverse, OUP, 2012).

Moreover, according to quantum field theory, elementary particles such as electrons are merely excited states of underlying quantum fields. This in itself should undermine confidence in the fundamentality of so-called elementary particles, but unfortunately quantum field theory provides a rather sparse characterisation of what a quantum field actually is, merely specifying it to be a self-adjoint operator-valued field on space-time (technically an operator-valued 'distribution'). The significance of quasi-particles is that they provide a very concrete substrate upon which particle-like entities can be realised, and a discrete substrate at that.

Perhaps, then, there is no lowest level to the structure of the universe; no foundations and no basement level, just an infinite multi-storey subterranean car-park.

Wednesday, September 19, 2012

﻿﻿﻿﻿﻿﻿﻿﻿﻿﻿﻿﻿﻿﻿﻿There was a suggestion on this blog at the beginning of the season that Mercedes's DRS-activated F-duct might be utilising more than one means to reduce straightline drag.

In this context, Adrian Newey recalls that in the early 1990s, when active suspension was permitted, "We realised in the wind-tunnel that if we lowered the rear and raised the front, you could stall the diffuser and that reduced the drag of the car significantly...I can't remember the figure but that would give them something like an extra 10 kph," (p233-234 in Williams, Maurice Hamilton, 2009). ﻿﻿﻿﻿﻿

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Stalling the front-wing not only reduces drag, but by virtue of reducing front downforce also increases front ride-height. Hence, using DRS to stall the front-wing could, in principle, also stall the diffuser.

Admittedly, diffuser dimensions were somewhat different in the early 1990s, and there hasn't been any suggestion from rival engineers this year that Mercedes are indeed exploiting this mechanism. It would, for a start, require a car very softly sprung in dive. Nevertheless, it's interesting to look at the ride-height map above, reproduced from Toet, Zhang and Zeridan's 2006 paper, Ground Effect Aerodynamics of Racecars.

The top diagram provides the front downforce contour map, while the image at the bottom offers the rear downforce contours. In each case, front ride-height is on the vertical axis, and rear ride-height is on the horizontal.

It can be seen that front downforce is maximised when the car has maximum rake, with a low front ride-height and a high rear ride-height. This is simply because the front-wing operates in ground-effect. Rear downforce, however, is slightly more subtle because the diffuser downforce is dependent upon (i) the strength of the side-edge vortices, and (ii) the prevention of turbulent ingress from the rotating rear wheels. As the rear ride-height lowers, downforce increases up to a certain point, but if the car goes any lower, the side-edge vortices dilate and weaken, and the diffuser stalls. There is therefore something of an escarpment in the rear downforce contour map.

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The other feature of interest in this rear downforce map is the sheer cliff evident when the front ride-height increases to about 30mm. This may be the behaviour Adrian Newey was exploiting in the early 1990s. Sadly, no indication is given of the provenance of these diagrams; they are referred to merely as the downforce contours for a 'generic open wheeled race car'.

﻿﻿One might wish to compare and contrast with some actual ride-height maps for the F1-2000 Ferrari, (Ferrari Formula 1, Peter Wright, David Bull Publishing, p120), reproduced on the left here. One can see the same diagonal pattern to the front downforce contours, and a similar rear downforce plateau. Sadly, these diagrams don't extend up to a front ride-height of 30mm, so it's not possible to discern if the diffuser of an F1 car from the early 2000s could be stalled by raising the front ride-height.

As to what the current state-of-play is, these are questions which can, perhaps, only be answered by a tweet from Lewis Hamilton.